The long-term objective of the project is to regulate biological systems with light, an "on" and "off" photoswitch. For example, blue light would turn the system "on" and yellow light would turn the system "off." Turning the system "on" and "off" would be a result of a change in the molecular structure. Molecular structure is important in molecular recognition events including cellular recognition and metabolism, which are responsible for diseases such as cancer and diabetes. The specific objective of the grant is to determine the feasibility of using fulgimides, a class of photochromic organic molecules, as photoswitches in biological systems. Fulgimides change from a flexible open structure to a rigid closed structure when blue light is used and then revert back again with yellow light. Fulgimides are robust photoswitches as they can go back and forth repeatedly with little degradation and are stable in aqueous solutions. In addition, they turn "on" all the way and turn "off" almost all the way or vice versa. Specific Aims are: (1) Synthesize fulgimides with two reactive groups for incorporation into polymers and proteins. If the fulgimide is attached at two points, it will have more profound consequences when it changes from the "on" to the "off" state as opposed to when it is attached at only one point. (2) Characterize the photochemical properties of each novel compound. The photostationary state or how far "on" and "off" the molecule will turn will be determined at several wavelengths in various environments. (3) Incorporate fulgimides into polymers and proteins and apply them to biochemical problems. Fulgimides will be used to regulate enzyme activity. Enzymes will be imbedded in a polymer crosslinked with fulgimides. By illuminating with light the polymer's conformation will change, which will then alter the accessibility of the enzyme's active site. Polymers crosslinked with fulgimides will also be used in microfluid devices, "lab on a chip," to alter flow rates by changing pore size. In addition, fulgimides will be used to target specific enzymes by covalently connecting them to an active site directed inhibitor and an NHS ester which should react with a lysine group close to the active site. Upon illumination the inhibitor will in some cases be removed from the active site of the enzyme, thus reactivating its catalytic activity. Photochromic switches can be used to improve diagnostic kits ("lab on a chip") and the production of pharmaceuticals using enzymes, and for targeting particular cellular locations for therapy.